This invention relates to periodic sequence generators.
It is well known that two level pseudorandom (periodic) sequences may be achieved with logic circuits operating in modulo 2 arithmetic arranged in a feedback combination with binary shift registers. Multilevel pseudorandom sequences, however, are less common. Multilevel sequences may be achieved by grouping preselected portions of binary pseudorandom sequences, and by considering the groupings as representative of multilevel binary signals. Alternatively, a plurality of parallel binary shift registers may be used, and their output signals may be manipulated in modulo 2.sup.N arithmetic (where N is the number of shift registers) to also form a multilevel output signal. The later approach is diclosed by Nakamura in U.S. Pat. No. 3,780,275 issued Dec. 18, 1973, for modulo p.sup.N arithmetic where p is a prime number.
The above approaches to pseudorandom signal generation provide only a single maximum length sequence rather than a large number of prescribed sequences, and control of the waveform characteristics is nonexistent. Additionaly, the use of available memory by the above approaches is not necessarily optimal.